Hey Helen,
this will probably need a bit of Python.
Just to be clear: What type of "merge" are you talking about? Let's say we have two overlapping polygons in 2 layers:
Is your desired output the result of the Merge geoprocessing tool? This will combine multiple tables, each row of each table will be copied without editing. (Selection to show that they still overlap)
Or do you want the result of the geoprocessing tool Union? This works similar to Merge, but it creates the intersections as extra polygons. (Selection to show that the original polygons have been edited)
Or do you want the result of the editing tool Merge? This takes 2 geometries and turns them into one.
Or do you want something else?
Have a great day!
Johannes